(1) Field of the Invention
The present invention relates to a heating apparatus in which leakage of hot air from the interior of the furnace is markedly reduced even when a material to be heated is charged into or delivered out of the heating furnace.
(2) Description of the Prior Art
In conventional heating apparatus, an inlet or outlet for a material to be heated is kept open or doors are mounted for the inlet and outlet.
In these conventional heating apparatuses, the entire length of the furnace is increased so that even if the temperature is lowered in the vicinity of the inlet or outlet, the change of the temperature is eliminated or reduced in the central portion of the furnace.
If the length of the furnace is thus increased, a large quantity of a furnace-constituting material must be used and the manufacturing cost of the furnace is increased. Moreover, a large area is necessary for construction of such heating apparatus, and the scale of the entire equipment including this heating apparatus is inevitably increased.
Especially in case of a heating apparatus for use in manufacture of carbon electrodes to be used for a metal melting electric furnace, this problem is very serious because a material to be heated, namely a graphite electrode, has considerable size and weight (for example, such graphite electrode has a diameter of 60 cm and a length of 200 cm).
When such material to be heated is charged into or delivered from the heating apparatus by means of a conveyor device or the like, the changing or delivery movement is performed at a low speed because the weight of the material is heavy. Accordingly, the door at the inlet or outlet of furnace must be opened for a long time.
Furthermore, when graphite electrodes are heated by the above-mentioned conventional heating apparatus, the length of the furnace must be remarkably increased.
Accordingly, it has been eagerly desired to develop a heating apparatus in which the furnace length can be reduced and the temperature in the furnace can be maintained at a high level during the charging or delivery operation even if the furnase length is shortened.